Posts Tagged: tolerance
Three citrus trees that produce inedible fruit at the UC Lindcove Research and Extension Center in Visalia may be a game-changer for the citrus industry, reported Ezra David Romero on Valley Public Radio.
The trees are thought to be resistant to huanglongbing, a severe disease of citrus that has devastated the Florida industry and could become a serious problem in California. The citrus-saving potential of the three 34-year-old trees was outlined in an article by UC Agriculture and Natural Resources writer Hazel White in the most recent issue of California Agriculture journal.
UC Riverside citrus breeder Mikeal Roose collected seed from the trees and will test seedlings as soon as they are large enough.
"So what (breeders) have to do is cross this with some edible varieties and eventually create something that has the gene for resistance, but also the genes for good fruit," said Beth Grafton-Cardwell, Lindcove director and research entomologist.
Huanglongbing disease has cut citrus production in Florida by more than half. It's been found in residential citrus trees in Southern California, but hasn't reached the state's vast commercial orchards yet. Grafton-Cardwell said she expects the disease will arrive in 4 or 5 years.
Ed Stover and crew at USDA, Fort Pierce in Florida have been studying the response of different scions and rootstocks that have been inoculated with the HLB bacteria. As reported in the Proceedings of the International Citrus Conference (http://www.icc2016.com/images/icc2016/downloads/Abstract_Book_ICC_2016.pdf), they have found some scion/rootstock combinations more tolerant or less susceptible to the disease six years after they have been inoculated. It turns out scions with a citron pedigree have more resistance. Also those with a Poncirus (trifoliate) background also had lower populations of the bacterium.
What this means is that there is resistance and possible immunity out there and there is breeding/genetic engineering material out there that can be used to improve the whole of the citrus family to HLB. Of course, this will take time, but there is hope.
HLB symptoms and trifoliate leaves
Recently, I read an article in "Fresh Plaza" about the arrival of large amounts of 'Kinnow' mandarin fruit from Pakistan. http://www.freshplaza.com/article/117470/Discover-Pakistani-kinnow-mandarins-at-Fruit-Logistica-2014#SlideFrame_1
This is a country that is surrounded by countries with huanglongbing. It's also the country where Mark Hoddle, Biocontrol Specialist from UC Riverside, collected Tamarixia radiata , the tiny wasp that is helping control Asian Citrus Psyllid. Pakistan has invested heavily in juice plants just for this industry which was established with this selection that came out of the Citrus Research Station breeding program in the 1930's. It makes me wonder if there might be a significant tolerance to this citrus disease in this mandarin variety. There has been a lot of work by both USDA and U. of Florida evaluating citrus varieties for tolerance to HLB. A wide range of tolerances have been noted. Fred Gmitter along with others are involved with this work and find that under different climatic conditions, resistance can vary. In the 'Kinnow' variety, it looks like there is hope in finding a variety that can be used to breed tolerance into other varieties. The fruit itself is noted for its juiciness and sweetness. But as you can see from the photo, it's got a lot of seeds.